1. Field of the Invention
The invention relates to a circuit for supervising the degree of wear of commutator-contacting carbon brushes of a direct current electric motor of an electrically operated vehicle, particularly of a forklift, powered by an accumulator, wherein the carbon brushes carry electrically insulated control brushes movable therewith, and wherein a warning signal indicator is connected to the control brushes, which provides a selectable optical and acoustic warning signal, when the control brushes establish contact with the commutator upon a predetermined degree of wear of the carbon brushes, the warning signal indicator being switched into the circuit upon establishment of such a contact.
2. Description of the Prior Art
In conventional circuits of this type, the warning signal indicator substantially consists of a signaling light, which is connected between the control brushes and one pole of an accumulator of the electrically operated vehicle. When the commutator carbon brushes are worn, the control brushes close the circuit of the signaling light through the armature of the electric motor to the other pole of the accumulator. As the commutator potential changes when the motor is subjected to a fluctuating load, the light intensity of the conventionally used signaling light fluctuates also. The motor circuit is controlled by a gate or an electronic switch, and is interrupted when the vehicle comes to a stop. Consequently, the warning signal light is not operative in those situations during which the driver should concentrate on the indication provided by that warning signal indicator.